Manufacturing method of semiconductor devices

ABSTRACT

An element isolation method of a semiconductor device comprises the steps of forming an oxide film on a semiconductor substrate; forming a nitride film on the oxide film; forming an isolation trench on the semiconductor device, the isolation trench being formed through the nitride film and oxide film; forming an oxide insulation layer on the semiconductor substrate to fill the isolation trench and cover the nitride film; flattening the surface of the semiconductor substrate to expose the nitride film by removing a surface portion of the oxide insulation layer in the isolation trench and the oxide insulation layer on the nitride film; heating the flattened semiconductor substrate in a nitrogen-containing gas atmosphere under reduced pressure to form an oxy-nitride film at an interface between an inside wall of the isolation trench and the oxide insulation layer in the isolation trench; and removing the nitride film and the oxide film on the semiconductor substrate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a manufacturing method ofsemiconductor devices, in particular to an element isolation method on asubstrate in terms of STI (Shallow Trench Isolation) method.

[0003] 2. Description of the Related Art

[0004] In a semiconductor device, on a semiconductor substrate,constituent elements such as a transistor or diode, a capacitor, aresistance or the like are disposed to be electrically isolated fromeach other, these elements being interconnected with each other throughwirings.

[0005] Recently, with higher integration and higher speed of thesemiconductor devices, there is a strong demand for an improvement inthe technique isolating these elements from each other.

[0006] In isolating the elements, in view of realizing excellent elementcharacteristics, reliability and circuit performance, it is stronglydesired to, while flattening a surface as much as possible, simplifyingmanufacturing steps and decreasing defect density, make an elementisolation distance as small as possible.

[0007] The element isolation technique is roughly divided into LOCOS(Local Oxidation of Silicon) method and STI (Shallow Trench Isolation)method.

[0008] The LOCOS method where semiconductor substrate surface isselectively oxidized accompanies problems of erosion of an elementformation region due to an occurrence of so-called bird's beak and of anoccurrence of crystal defects due to an occurrence of local stressduring formation of field oxide.

[0009] On the contrary, the STI method is advantageous inminiaturization. In specific, after forming a trench in an elementisolation region by the RIE (reactive ion etching) method or the like,an oxide film as a filled material is deposited by the CVD (chemicalvapor deposition) method for instance. The oxide layer deposited on aportion other than the trench is removed and flattened by use of CMP(chemical mechanical polishing method) to perform the element isolation.

[0010] A convnetional STI method will be explained with reference toFIGS. 8 to 11. On a silicon substrate 1, a silicon oxide film 2 and asilicon nitride film 3 are sequentially formed, thereafter by use oflithography technique and dry etching technique, with the siliconnitride film 3 as a protective layer, a silicon isolation trench 8 isformed. Thereafter, by of the CVD method, a second silicon oxide layer 4is diposited in the silicon isolation trench 8 to fill the trench. Thestate up to this step is shown in FIG. 8.

[0011] Next, as shown in FIG. 9, the silicon oxide layer 4 is flattenedby use of the CMP method, thereafter the silicon nitride film 3 that isa protective layer and the first silicon oxide film 2 being removed.Then, the filed silicon oxide layer 4 is thermally treated to form a STIisolation region.

[0012] In the conventional STI like the above, in removing the siliconoxide film 2, an etching liquid such as BHF is usually used. However,the etching liquid permeates into an interface between the siliconsubstrate 1 and the filled silicon oxide layer 4 to result in a rapidetching at the interface. As a result, as shown in FIG. 10, a divot 7occurs.

[0013] A final thermal treatment is performed to densify. However,because of an oxidizing atmosphere, silicon tends to be oxidized, as aresult, as shown in FIG. 10, the STI region undergoes changes. That is,the width of the isolation trench 8 (conversion difference) becomeslarger to result in a difficulty in miniaturizing.

[0014] Further, after forming the isolation region, an impurity (P or B)is introduced in the element formation region to form a transistor.However, as shown in FIG. 11, through the second filled oxide layer 4from the trench portion, the impurity diffuses to the external to resultin a decrease of the impurity concentration.

[0015] In order to overcome the aforementioned disadvantages, JapanesePatent Laid-open Application No. HEI 11-3936 discloses an elementisolation method for semiconductor devices. In which, on a wall surfaceof an isolation trench a silicon oxide film is formed by thermaloxidation, or further on the silicon oxide film formed on the wallsurface of the trench a silicon nitride film is deposited. Then, asilicon oxide film is deposited on the substrate by the CVD method,further heat treating the entire substrate in a high-pressureatmosphere.

[0016] Further, Japanese Patent Laid-open Application No. HEI 11-45996discloses a method for manufacturing semiconductor devices. In which, asilicon substrate is directly nitrided, or with a silicon nitride filmas a mask nitrogen ions are selectively injected into an isolationtrench sidewall or a bottom surface thereof, to diffuse nitrogen atomsinto the silicon substrate. Due to the action of the nitrogen atoms,channel impurities are suppressed from diffusing into the trench filledoxide layer.

[0017] However, when a nitride film is deposited between the filledoxide layer and the silicon substrate, the nitride film, having atendency of easily trapping charges, is liable to affect electricallyadversely on a transistor.

[0018] As mentioned above, in the conventional STI, there have beenproblems that the divot occurs at an upper interface between the siliconsubstrate and the filled oxide layer and due to the large isolationwidth the miniaturization becomes difficult. Further, there is alikelihood that the impurity doped after formation of the isolationregion goes therethrough to lower the impurity concentration to resultin deteriorating element characteristics. When inserting a nitride filmbetween the silicon substrate and the filled oxide layer to overcomethese problems, there occurs a new problem that due to the charge trapan electrically adverse influence is caused.

SUMMARY OF THE INVENTION

[0019] An object of the present invention, which is performed to solvethe aforementioned problems, is to provide an element isolation methodof a semiconductor device that can realize high miniaturization and isexcellent in electrical reliability.

[0020] The element isolation method of the present invention ischaracterized in that an oxynitride film is formed at an interfacebetween a substrate and a filled oxide film.

[0021] A first method for manufacturing a semiconductor device of thepresent invention comprises the steps of forming an oxide film on asemiconductor substrate; forming a nitride film on the oxide film;forming an isolation trench on the semiconductor device, the isolationtrench being formed through the nitride film and oxide film; forming anoxide insulation layer on the semiconductor substrate to fill theisolation trench and cover the nitride film; flattening the surface ofthe semiconductor substrate to expose the nitride film by removing asurface portion of the oxide insulation layer in the isolation trenchand the oxide insulation layer on the nitride film; heating theflattened semiconductor substrate in a nitrogen-containing gasatmosphere under reduced pressure to form an oxy-nitride film at aninterface between an inside wall of the isolation trench and the oxideinsulation layer in the isolation trench; and removing the nitride filmand the oxide film on the semiconductor substrate.

[0022] A second method for manufacturing a semiconductor device of thepresent invention comprises the steps of forming a first oxide film on asemiconductor substrate; forming a nitride film on the first oxide film;forming an isolation trench on the semiconductor substrate, theisolation trench being formed through the nitride film and first oxidefilm; forming a second oxide layer on a surface of the isolation trench;heating the semiconductor substrate having the isolation trench in anitrogen-containing gas atmosphere under reduced pressure to form anoxy-nitride film on a surface of the isolation trench; forming an oxideinsulation layer on the semiconductor substrate to fill the isolationtrench and cover the nitride film; flattening a surface of thesemiconductor substrate by removing a surface portion of the oxideinsulation layer in the isolation trench and the oxide insulation layeron the nitride film; and removing the nitride film and the first oxidefilm on the semiconductor substrate.

[0023] In the method for manufacturing a semiconductor device of thepresent invention, an oxynitride film is formed due to an introductionof nitrogen into an interface between the isolation trench and the oxideinsulating layer. Alternatively, an oxynitride film is formed on thesurface of the formed isolation trench. In both cases, the thermaltreatment is performed in an atmosphere of nitrogen containing gasselected from a group consisting of NO, N₂O, NO₂ and NH₃. Preferably,when heat treating is performed in NO or N₂O gas containing atmosphere,an oxynitride film, which has nitrogen concentration peak at theneighborhood of the interface between the isolation trench and the oxideisolating layer, is formed.

[0024] Further, heating is performed in an atmosphere of reducedpressure such as for instance approximately 4 Torr to 400 Torr. In thatcase, at the interface between the isolation trench of the siliconsubstrate and the filled oxide insulating layer, nitrogen concentratesto form a preferable oxynitride film.

[0025] The oxynitride film, being low in an etching rate by HF or thelike compared with that of the oxide film, can suppress an abnormaletching (occurrence of divot) from occurring at the interface betweenthe trench and the insulating layer. As a result, a isolation regionhaving a flat surface can be formed.

[0026] Further, the oxynitride film is dense in its structure andexcellent in its barrier characteristics. Accordingly, after formationof the element isolation trench, when being thermally treated even in anoxidizing gas atmosphere, the oxynitride film protects the siliconthereunder from being oxidized. As a result, the aforementioned notintended dimensional error such as the trench width change due to thethermal treatment (occurrence of conversion difference), can beprevented from occurring to result in realization of an accurateminiaturization.

[0027] Further, after the STI processing, when forming a transistor, onthe silicon substrate of an element region located between an elementisolation region and an element isolation region the impurities such asboron (B), phosphorus (P) or the like are doped. In that case, theoxynitride film blocks diffusion of these impurities to result inpreventing concentration from varying due to the diffusion ofimpurities.

[0028] Further, the step of heating the substrate in anitrogen-containing gas atmosphere of the present invention alternateswith the step of densifying after the CVD depositing. Accordingly, thenumber of the steps can be decreased to result in a realization of lowcosts.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a sectional view showing one step in a first elementisolation method of a semiconductor device of the present invention.

[0030]FIG. 2 is a sectional view showing one step in a first elementisolation method of a semiconductor device of the present invention.

[0031]FIG. 3 is a sectional view showing one step in a first elementisolation method of a semiconductor device of the present invention.

[0032]FIG. 4 is a sectional view showing one step in a first elementisolation method of a semiconductor device of the present invention.

[0033]FIG. 5 is a sectional view showing one step in a second elementisolation method of a semiconductor device of the present invention.

[0034]FIG. 6 is a sectional view showing one step in a second elementisolation method of a semiconductor device of the present invention.

[0035]FIG. 7 is a sectional view showing one step in a second elementisolation method of a semiconductor device of the present invention.

[0036]FIG. 8 is a sectional view showing one step of a conventionalelement isolation method of a semiconductor device.

[0037]FIG. 9 is a sectional view showing one step of a conventionalelement isolation method of a semiconductor device.

[0038]FIG. 10 is a sectional view showing one step of a conventionalelement isolation method of a semiconductor device.

[0039]FIG. 11 is a sectional view showing one step of a conventionalelement isolation method of a semiconductor device.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] In the following, with reference to the drawings, embodiments ofthe present invention will be explained.

Embodiment 1

[0041] On a silicon semiconductor substrate 11, in terms of thermaloxidation a silicon oxide film 12 of a thickness of approximately 50 nmis formed as an insulating layer, further thereon in terms of the CVDmethod a silicon nitride film 13 of a thickness of approximately 150 nmbeing deposited.

[0042] In that case, the silicon nitride film 13 and the silicon oxidefilm 12, by the lithography technique and dry etching technique, arepatterned into a desired trench shape.

[0043] Next, with the patterned silicon nitride film 13 as a protectivelayer, the silicon of the substrate 11 is dry etched to form a trench 18of a width of approximately 0.5 nm and a depth of approximately 0.2 to0.4 nm. The etching here is performed by, for instance, the reactive ionetching (RIE).

[0044] Further, by using the CVD method, as a filled insulator of theSTI (shallow trench isolation) a second silicon oxide layer 14 isdeposited. The state up to here is shown in FIG. 1. The silicon oxidelayer 14 is deposited to fill the trench 18 and to cover the siliconnitride film 13.

[0045] When the silicon oxide layer is used for the filled insulator, asgas material for CVD, as inorganic starting materials, silicontetrachloride (SiCl₄), dichlorosilane (SiH₂Cl₂), mono-silane (SiH₄) orthe like can be used. From these gases, a HTO (High Temperature Oxide)film that can be formed at a high temperature (approximately 750 to 900°C.) and a LTO (Low Temperature Oxide) film that can be formed at a lowtemperature (approximately 400° C.) are formed depending on necessaryproperties.

[0046] Further, as an organic starting gas for CVD silicon oxide layer,tetraethoxysilane TEOS [Si(OC₂H₅)₄], tetramethoxysilane TMOS[Si(OCH₃)₄], tetrapropoxysilane TPOS [Si(OC₃H₇)₄],diacetoxyditertiarybutoxysilane DADBS [Si(CH₃COO)₂(C₄H₉O)₂] or the likecan be used. With these organic gases as the CVD material, a siliconoxide layer also can be formed.

[0047] Furthermore, not only the aforementioned silicon oxides but alsophosphosilicate glass PSG [(SiO₂)_(x)(P₂O₅)_(1−x)], borosilicate glassBSG [(SiO₂)_(x)(B₂O₃)_(1−x)] and borophosphosilicate glass BPSG[(SiO₂)_(x)(P₂O₅·B₂O₃)_(1−x)] can be used as demands arise.

[0048] As the CVD methods that can be used, atmospheric pressure CVDmethod, low pressure CVD method, plasma CVD method, photo CVD method,liquid phase CVD method or the like can be cited.

[0049] In the atmospheric pressure and low pressure CVD methods, ozoneCVD method where O₂ is introduced in an ozonizer to form ozone (O₃) dueto discharge can be used. In the low pressure CVD method, for instance,TEOS and ozone O₃ are allowed to react under a reduced pressure ofapproximately 6.7 kPa to deposit a silicon oxide layer.

[0050] The deposition of an oxide layer by the plasma CVD can beperformed by use of plasma discharge at for instance 13.56 MHz orapproximately 150 kHz with gas sources such as TEOS, O₂, He or the like.

[0051] In the deposition of an oxide layer by the photo CVD, lightenergy of mainly ultra-violet light is used to cause a photoreaction.The light energy of mainly ultra-violet light can be obtained fromexcimer lasers such as ArF (wavelength; 193 nm), KrF (wavelength; 249nm), XeCl (wavelength; 308 nm), XeF (wavelength; 350 nm) or the like,high pressure mercury lamp and mercury-xenon lamp

[0052] The deposition by the liquid phase CVD method, with for instanceO₂ excited due to RF discharge and TMS (tetramethylsilane), is performedat −40° C.

[0053] The aforementioned CVDs are performed in a gas of for instancereductive gases such as H₂ or the like, inert gases such as He, Ne, Ar,Kr and Xe, O₂, N₂, HCl, CO or CO₂, or in a gas mixture of two kinds ormore of the gases selected therefrom.

[0054] Next, as shown in FIG. 2, by use of CMP technique, the flatteningis implemented to expose the silicon nitride protective film 13. Theflattening is performed by, for instance, the CMP (chemical mechanicalpolishing).

[0055] After the flattening, with BHF (a liquid mixture of HF and NH₄F),the oxide portion of the trench is adjusted in the height thereof.

[0056] Next, in a reduced pressure NO gas atmosphere of approximately400Torr, thermal treatment is performed at a temperature of 750° C. for60 min. The step of oxynitridation is performed under the processconditions of NO/N₂ gas ratio of {fraction (1/9)} slm, 15 minutes at aconcentration of 1.0×10¹⁴ atom/cm², 30 minutes at a concentration of1.6×10¹⁴ atom/cm² and 15 minutes at a concentration of 1.8×10¹⁴atom/cm².

[0057] Due to the nitridation, in the neighborhood of the interfacebetween the oxide layer 14 in the trench 18 and the silicon substrate 1nitrogen 15 is introduced to form, as shown in FIG. 3, an oxynitridefilm nearly equal to nitride film. In particular, at the interfacebetween the silicon 1 and the oxide layer 14, high concentrationnitrogen 15 is trapped.

[0058] Thereafter, as shown in FIG. 4, the silicon nitride film 13 andsilicon oxide film 12 are removed and further by BHF etching the STIshape is adjusted. The etching rate by BHF of the oxynitride film of theportion that is oxynitrided due to the thermal oxynitridation becomessmaller than that of the oxide film. The degree thereof can be adjustedthrough the conditions of the thermal oxynitridation.

[0059] In the aforementioned thermal oxynitridation, NO gas is used.However, other than the NO gas, with nitrogen oxides such as NO₂, N₂O orthe like and other gases such as NH₃ gas or the like, or a gas mixturethereof, the thermal oxynitridation can be similarly performed.

Embodiment 2

[0060] Similarly with Embodiment 1, as shown in FIG. 5, a trench 18provided with a silicon oxide film 12 that is a first oxide film and asilicon nitride protective film 13 is formed.

[0061] Next, as shown in FIG. 6, on the inner wall of the trench, athermal oxide film 16 of a thickness of approximately 5 nm is formed.

[0062] Later, as shown in FIG. 7, the oxynitridation is performed atapproximately 800° C. in an NO gas containing atmosphere under a reducedpressure of 4 Torr to deposit an oxynitride film 17. The processconditions for the oxynitridation are as follows. The NO/N₂O gas ratiois {fraction (1/9)} slm, 15 minutes at a concentration of 1.0×10¹⁴atom/cm², 30 minutes at a concentration of 1.6×10¹⁴ atom/cm² and 15minutes at a concentration of 1.8×10¹⁴ atom/cm².

[0063] Thereafter, though not shown in particular in the drawing, a CVDoxide film is filled as an insulating layer to implement trench elementisolation similarly with embodiment 1.

[0064] Instead of the NO gas, nitrogen oxide gases such as NO₂, N₂O orthe like and other gases such as NH₃ or the like, or a combinationthereof may be used. Further, the oxynitridation with these gases may beperformed, without through the thermal oxide film 16, directly on asurface of the trench silicon.

[0065] In all of the aforementioned embodiments, due to the thermaltreatment, the oxynitride film 17 is formed on an inner wall surface ofthe trench. However, after formation of the silicon trench, bydepositing the oxynitride film by the plasma processing, a similareffect can be expected.

[0066] According to the present element isolation method of asemiconductor device, the oxynitride film, being low in the etching rateby HF compared with that of the oxide film, can suppress abnormaletching, namely divots, from occurring at an interface between thesilicon in the element formation region and the insulator filled in theelement isolation trench. Thereby, an isolation region of flat surfacecan be formed. Similarly, the oxynitride film, being dense in structureand excellent in barrier characteristic, can protect the siliconsubstrate from being oxidized to form the isolation region withaccuracy. Further, even after the formation of the element isolationregion, the oxynitride film can effectively block the doped impuritiesfrom diffusing into the element isolation region.

[0067] Further, according to the present invention, the formation of theoxynitride film at an interface between the inner wall of the trench andthe filled oxide insulating layer is performed by heating in anatmosphere including nitrogen of reduced pressure of less than 1 atm.Accordingly, the oxynitride film can be efficiently and intensivelyformed at the interface.

[0068] Thus, according to the element isolation method of the presentinvention, high miniaturization and excellent electrical reliability canbe realized at low costs and with simplicity.

[0069] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A method for manufacturing a semiconductordevice, comprising the steps of: forming an oxide film on asemiconductor substrate; forming a nitride film on the oxide film;forming an isolation trench on the semiconductor device, the isolationtrench being formed through the nitride film and oxide film; forming anoxide insulation layer on the semiconductor substrate to fill theisolation trench and cover the nitride film; flattening the surface ofthe semiconductor substrate to expose the nitride film by removing asurface portion of the oxide insulation layer in the isolation trenchand the oxide insulation layer on the nitride film; heating theflattened semiconductor substrate in a nitrogen-containing gasatmosphere under reduced pressure to form an oxy-nitride film at aninterface between an inside wall of the isolation trench and the oxideinsulation layer in the isolation trench; and removing the nitride filmand the oxide film on the semiconductor substrate.
 2. The method formanufacturing a semiconductor device according to claim 1 , wherein thenitrogen containing gas atmosphere comprises at least one selected fromthe group consisting of NO, N₂O, NO₂ and NH₃.
 3. The method formanufacturing a semiconductor device according to claim 1 , wherein thereduced pressure of the nitrogen-containing atmosphere is less than 1atm.
 4. A method for manufacturing a semiconductor device, comprisingthe steps of: forming a first oxide film on a semiconductor substrate;forming a nitride film on the first oxide film; forming an isolationtrench on the semiconductor substrate, the isolation trench being formedthrough the nitride film and first oxide film; forming a second oxidelayer on a surface of the isolation trench; heating the semiconductorsubstrate having the isolation trench in a nitrogen-containing gasatmosphere under reduced pressure to form an oxy-nitride film on asurface of the isolation trench; forming an oxide insulation layer onthe semiconductor substrate to fill the isolation trench and cover thenitride film; flattening a surface of the semiconductor substrate byremoving a surface portion of the oxide insulation layer in theisolation trench and the oxide insulation layer on the nitride film; andremoving the nitride film and the first oxide film on the semiconductorsubstrate.
 5. The method for manufacturing a semiconductor deviceaccording to claim 4 , wherein the nitrogen containing gas atmospherecomprises at least one selected from the group consisting of NO, N₂O,NO₂ and NH₃.
 6. The method for manufacturing a semiconductor deviceaccording to claim 4 , wherein the reduced pressure of thenitrogen-containing atmosphere is less than 1 atm.